This invention relates to a resist composition comprising a hydrogenated product of ring-opening metathesis polymer as a base resin, especially having improved sensitivity, resolution, and etching resistance and suited for semiconductor microfabrication using UV and deep-UV radiation (inclusive of excimer lasers), and a patterning process using the resist composition.
Semiconductor integrated circuits have reached so great a scale of integration that large scale integrated circuits (LSI) and very large scale integrated circuits (VLSI) are now used in practice. At the same time, the minimum pattern size of integrated circuits reaches the submicron region and will become finer. Micropatterning is generally carried out by lithography, for example, by forming a thin film on a substrate, coating a resist thereon, effecting selective exposure to form a latent image of the desired pattern, developing the resist to form a resist pattern, effecting dry etching using the resist pattern as a mask, and removing the resist, leaving the desired pattern.
The light source used for exposure in the lithography is ultraviolet radiation, typically g-line (wavelength 436 nm) and i-line (wavelength 365 nm). As the pattern feature size becomes finer, the light source undergoes a transition to shorter wavelength ones such as deep-UV, vacuum-UV, electron beams (EB) and x-rays. The latest stage of lithography considers to use as the exposure light source excimer lasers, specifically KrF laser of wavelength 248 nm and ArF laser of wavelength 193 nm. The excimer lasers are expected to be effective for micropatterning.
In resist compositions for forming submicron-size patterns using exposure light of shorter wavelength or in the vacuum ultraviolet region, a variety of polymers or copolymers are used. Proposed thus far are polymers or copolymers of acrylic esters or alpha-substituted acrylic esters having an adamantane skeleton and acid-eliminatable protective groups in the ester moiety (see JP-A 4-39665), polymers or copolymers of acrylic esters or alpha-substituted acrylic esters having a norbornane skeleton and acid-eliminatable protective groups in the ester moiety (see JP-A 5-257281), polymers or copolymers of cyclohexylmaleimide (see JP-A 5-257285), polymers having a cellulose skeleton in the backbone which undergoes cleavage with acid (see JP-A 6-342212), and polyvinyl alcohol and polyvinyl alcohol derivatives (see JP-A 7-333850).
These polymers and copolymers do not satisfy all the characteristics necessary as resist material including dry etching resistance, transparency to deep-UV, solubility in resist solvents, wettability with developers, adhesion to silicon and other substrates, and solubility in stripping agents. None of them are easy to synthesize. There is a need to have polymers satisfying the above requirements.
On the other hand, photoresist compositions comprising polymers based on aliphatic cyclic hydrocarbon as the backbone and having a cyclic skeleton bearing acid-decomposable functional groups are disclosed in WO 97/33198, JP-A 9-230595, JP-A 9-244247, and JP-A 10-254139. These cyclic polymers have good dry etching resistance and transparency to deep-UV, but leave unsolved the problems of dissolution in resist solvents in high concentrations, wettability with developers, and adhesion to silicon substrates.
An object of the invention is to provide a resist composition which is sensitive to high-energy radiation, has improved sensitivity, resolution and etching resistance, and is useful in micropatterning using electron beams and deep-UV. Another object is to provide a micropatterning process using the same.
We have found that a hydrogenated product of a ring-opening metathesis polymer having a narrow molecular weight distribution is useful as the base resin in a positive acting photoresist composition because it satisfies all the above-described characteristics necessary for a polymer to perform as the base resin in a resist composition, more specifically characteristics including light transparency, high sensitivity, high resolution, and affinity to alkali developers, so that it is suitable for use in semiconductor micropatterning with UV and deep-UV (inclusive of excimer lasers) and can form a satisfactory pattern. Studying hydrogenated products of polymers resulting from ring-opening metathesis polymerization of cyclic olefin monomers to see whether they have a potential to utilize as the base resin to formulate resist compositions having improved optical properties, electric properties, high rigidity, heat resistance, substrate adhesion and weathering resistance, we have found that a hydrogenated product of a ring-opening metathesis polymer having specific structural units of aliphatic cyclic compound in the backbone, which cyclic structure partially contains oxygen atom-bearing structural units, satisfies all the characteristics necessary for resist material.
In a first aspect, the invention provides a resist composition comprising as a base resin a hydrogenated product of a ring-opening metathesis polymer comprising structural units [A] of the following general formula (1) and one or both of structural units [B] of the following general formula (3) and structural units [C] of the following general formula (4), and having a constitutional molar ratio defined as [A]/([B]+[C]) of from 20/80 to 99/1 and a dispersity defined as a weight average molecular weight (Mw) divided by a number average molecular weight (Mn) of 1.0 to 2.0.
Herein at least one of R1 to R4 is a functional group having a tertiary ester group of cyclic alkyl represented by the following general formula (2): 
wherein the broken line denotes a valence bond, R5 is selected from the class consisting of hydrogen, straight, branched or cyclic alkyl groups of 1 to 10 carbon atoms, straight, branched or cyclic alkoxyalkyl groups of 2 to 10 carbon atoms, and straight, branched or cyclic acyl groups of 1 to 10 carbon atoms, R6 is a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms, W1 is a single bond or (k+2)-valent hydrocarbon group of 1 to 10 carbon atoms, Z is a divalent hydrocarbon group of 2 to 15 carbon atoms which forms a single ring or bridged ring with the carbon atom, and k is 0 or 1.
The remainders of R1 to R4 are independently selected from the class consisting of hydrogen, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, halogen atoms, straight, branched or cyclic haloalkyl groups of 1 to 20 carbon atoms, straight, branched or cyclic alkoxy groups of 1 to 20 carbon atoms, straight, branched or cyclic alkoxyalkyl groups of 2 to 20 carbon atoms, straight, branched or cyclic alkylcarbonyloxy groups of 2 to 20 carbon atoms, arylcarbonyloxy groups of 6 to 20 carbon atoms, straight, branched or cyclic alkylsulfonyloxy groups of 1 to 20 carbon atoms, arylsulfonyloxy groups of 6 to 20 carbon atoms, straight, branched or cyclic alkoxycarbonyl groups of 2 to 20 carbon atoms, and straight, branched or cyclic alkoxycarbonylalkyl groups of 3 to 20 carbon atoms; X1, which may be the same or different, is xe2x80x94Oxe2x80x94 or xe2x80x94CR72xe2x80x94 wherein R7 is hydrogen or a straight or branched alkyl group of 1 to 10 carbon atoms; and j is 0 or an integer of 1 to 3.
Herein R8 to R11 each are independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms, X2, which may be the same or different, is xe2x80x94Oxe2x80x94 or xe2x80x94CR122xe2x80x94 wherein R12 is hydrogen or a straight or branched alkyl group of 1 to 10 carbon atoms, and m is 0 or an integer of 1 to 3.
Herein R13 to R16 each are independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms, X3, which may be the same or different, is xe2x80x94Oxe2x80x94 or xe2x80x94CR172xe2x80x94 wherein R17 is hydrogen or a straight or branched alkyl group of 1 to 10 carbon atoms, one of Y1 and Y2 is xe2x80x94(Cxe2x95x90O)xe2x80x94 and the other is xe2x80x94CR182xe2x80x94 wherein R18 is hydrogen or a straight or branched alkyl group of 1 to 10 carbon atoms, and n is 0 or an integer of 1 to 3.
At least one of X1 in the structural units [A] of formula (1), X2 in the structural units [B] of formula (3), and X3 in the structural units [C] of formula (4) is xe2x80x94Oxe2x80x94.
Preferably, the functional group having a tertiary ester group of cyclic alkyl of the formula (2) represented by at least one of R1 to R4 is 1-alkylcyclopentyl ester, 2-alkyl-2-norbornyl ester or 2-alkyl-2-adamantyl ester.
In one preferred embodiment, the hydrogenated product of ring-opening metathesis polymer further comprises structural units [D] of the following general formula (5). 
Herein at least one of R19 to R22 is a functional group having a carboxylic acid group represented by the following general formula (6): 
wherein the broken line denotes a valence bond, R23 is selected from the class consisting of hydrogen, straight, branched or cyclic alkyl groups of 1 to 10 carbon atoms, straight, branched or cyclic alkoxyalkyl groups of 2 to 10 carbon atoms, and straight, branched or cyclic acyl groups of 1 to 10 carbon atoms, W2 is a single bond or (q+2)-valent hydrocarbon group of 1 to 10 carbon atoms, and q is 0 or 1; the remainders of R19 to R22 are independently selected from the class consisting of hydrogen, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, halogen atoms, straight, branched or cyclic haloalkyl groups of 1 to 20 carbon atoms, straight, branched or cyclic alkoxy groups of 1 to 20 carbon atoms, straight, branched or cyclic alkoxyalkyl groups of 2 to 20 carbon atoms, straight, branched or cyclic alkylcarbonyloxy groups of 2 to 20 carbon atoms, arylcarbonyloxy groups of 6 to 20 carbon atoms, straight, branched or cyclic alkylsulfonyloxy groups of 1 to 20 carbon atoms, arylsulfonyloxy groups of 6 to 20 carbon atoms, straight, branched or cyclic alkoxycarbonyl groups of 2 to 20 carbon atoms, and straight, branched or cyclic alkoxycarbonylalkyl groups of 3 to 20 carbon atoms; X4, which may be the same or different, is xe2x80x94Oxe2x80x94 or xe2x80x94CR242xe2x80x94 wherein R24 is hydrogen or a straight or branched alkyl group of 1 to 10 carbon atoms; and p is 0 or an integer of 1 to 3.
More preferably, the hydrogenated product of ring-opening metathesis polymer has a constitutional molar ratio of structural units [A] of formula (1), structural units [B] of formula (3) and structural units [C] of formula (4) to structural units [D] of formula (5), defined as ([A]+[B]+[C])/[D], of from 100/0 to 20/80.
In a further preferred embodiment, the hydrogenated product of ring-opening metathesis polymer further comprises structural units [E] of the following general formula (7). 
Herein at least one of R25 to R28 is a functional group having a carboxylate group represented by the following general formula (8): 
wherein the broken line denotes a valence bond, R29 is selected from the class consisting of hydrogen, straight, branched or cyclic alkyl groups of 1 to 10 carbon atoms, straight, branched or cyclic alkoxyalkyl groups of 2 to 10 carbon atoms, and straight, branched or cyclic acyl groups of 1 to 10 carbon atoms, R30 is a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms, straight, branched or cyclic alkoxyalkyl group of 2 to 10 carbon atoms, or straight, branched or cyclic haloalkyl group of 1 to 20 carbon atoms, W3 is a single bond or (s+2)-valent hydrocarbon group of 1 to 10 carbon atoms, and s is 0 or 1; the remainders of R25 to R28 are independently selected from the class consisting of hydrogen, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, halogen atoms, straight, branched or cyclic haloalkyl groups of 1 to 20 carbon atoms, straight, branched or cyclic alkoxy groups of 1 to 20 carbon atoms, straight, branched or cyclic alkoxyalkyl groups of 2 to 20 carbon atoms, straight, branched or cyclic alkylcarbonyloxy groups of 2 to 20 carbon atoms, arylcarbonyloxy groups of 6 to 20 carbon atoms, straight, branched or cyclic alkylsulfonyloxy groups of 1 to 20 carbon atoms, arylsulfonyloxy groups of 6 to 20 carbon atoms, straight, branched or cyclic alkoxycarbonyl groups of 2 to 20 carbon atoms, and straight, branched or cyclic alkoxycarbonylalkyl groups of 3 to 20 carbon atoms; X5, which may be the same or different, is xe2x80x94Oxe2x80x94 or xe2x80x94CR312xe2x80x94 wherein R31 is hydrogen or a straight or branched alkyl group of 1 to 10 carbon atoms; and r is 0 or an integer of 1 to 3.
More preferably, the hydrogenated product of ring-opening metathesis polymer has a constitutional molar ratio of structural units [A] of formula (1), structural units [B] of formula (3) and structural units [C] of formula (4) to structural units [E] of formula (7), defined as ([A]+[B]+[C])/[E], of from 100/0 to 40/60.
Preferably, the hydrogenated product of ring-opening metathesis polymer has a number average molecular weight (Mn) of 500 to 200,000 and more preferably a number average molecular weight (Mn) of 3,000 to 20,000, as measured by gel permeation chromatography (GPC) using a polystyrene standard.
In another aspect, the invention provides a process for forming a resist pattern comprising the steps of applying the resist composition onto a substrate to form a coating, heat treating the coating and then exposing it to high-energy radiation or electron beams through a photo mask, and optionally heat treating the exposed coating and developing it with a developer.